The oxidation of polyethylene to form oxidized polyethylene has been known for many years. Oxidized polyethylene is useful in the formation of emulsions that can be used in many applications, these include: components in floor care products, lubricants for polymer processing, or lubricants for textile applications, as well as various other emulsion applications, such as in leather processing, water dispersible coatings, inks and resins.
One method of oxidizing polyethylene entails the oxidation of polyethylene in the melt phase. The melt phase oxidation of polyethylene has some limits, however, requiring that the oxygen-containing gas be readily defused at high concentrations through the molten polyethylene. If the polyethylene is too viscous, the oxygen diffusion is very slow and impractical on a commercial scale. Additionally, melt oxidation in some instances increases viscosity due to crosslinking, further decreasing the oxygen diffusion.
Melt phase conditions can be used to oxidize low density polyethylene. However, some forms of polyethylene, such as high density polyethylene are very difficult to oxidize due to their linear (unbranched) nature and a somewhat higher melting point. U.S. Pat. Nos. 3,332,711 and 5,064,908 both disclose the solid state oxidation of polyethylene in which particulate polyethylene is oxidized in a batch type process using oxygen containing gas and free radical initiator(s). Although the oxidation of polyethylenes that are difficult to oxidize in the melt phase can be conducted on particulate polyethylene according to the processes disclosed in these two patents, the oxidation entails extremely long process residence times.
It would be very desirable to be able to readily oxidize most polyethylenes, including the difficult to oxidize high density polyethylene, in a more rapid manner at reduced costs so as to more readily enable the commercial production of oxidized polyethylene.